During normal sinus rhythm (NSR), the heart beat is regulated by electrical signals produced by the sino-atrial (SA) node located in the right atrial wall. Each atrial depolarization signal produced by the SA node spreads across the atria, causing the depolarization and contraction of the atria, and arrives at the atrioventricular (A-V) node. The A-V node responds by propagating a ventricular depolarization signal through the bundle of His of the ventricular septum and thereafter to the bundle branches and the Purkinje muscle fibers of the right and left ventricles.
Atrial tachyarrhythmia includes the disorganized form of atrial fibrillation and varying degrees of organized atrial tachycardia, including atrial flutter. Atrial fibrillation (AF) occurs because of multiple focal triggers in the atrium or because of changes in the substrate of the atrium causing heterogeneities in conduction through different regions of the atria. The ectopic triggers can originate anywhere in the left or right atrium or pulmonary veins. The AV node will be bombarded by frequent and irregular atrial activations but will only conduct a depolarization signal when the AV node is not refractory. The ventricular cycle lengths will be irregular and will depend on the different states of refractoriness of the AV-node.
Sick sinus syndrome, also known as sinus node disease or sinus node dysfunction, is the name for a group of heart rhythm arrhythmias in which the sinus node doesn't work properly. Normally, the sinus node produces a steady pace of regular electrical impulses. In sick sinus syndrome, these signals are abnormally paced and therefore a person with sick sinus syndrome may have heart rhythms that are too fast, too slow, punctuated by long pauses—or an alternating combination of all of these rhythm problems. Many people with sick sinus syndrome eventually need a pacemaker to keep the heart in a regular rhythm. Therefore, what is needed is a method and apparatus for determining the occurrence of sick sinus syndrome of a patient in a cardiac monitoring device.